In this technical field, an IMT 2000 system is conventionally employed. In the conventional IMT 2000 system, a W-CDMA (Wideband-Code Division Multiple Access) scheme is premised, and a HSDPA (High Speed Downlink Packet Access) scheme, a HSUPA (High Speed Uplink Packet Access) scheme and other schemes are also employed. See 3GPP TS 25.308, “Technical Specification Group Radio Access Network; High Speed Downlink Packet Access (HSDPA); Overall description; Stage 2” and 3GPP TS 25.309, “Technical Specification Group Radio Access Network; FDD Enhanced Uplink; Overall description; Stage 2”, for example, regarding the conventional IMT 2000 system.
On the other hand, the W-CDMA standardization group 3GPP is studying the next generation mobile communication system. This system is called an Evolved-UTRA system or a LTE (Long Term Evolution) system. In this LTE system, OFDM (Orthogonal Frequency Division Multiplexing) and SC-FDMA (Single Carrier-Frequency Division Multiple Access) schemes are utilized as radio access schemes for downlinks and uplinks, respectively. For example, see 3GPP TS 36.211 (V8·0·0), September 2007.
The OFDM scheme is a multi-carrier transmission scheme where a frequency band is segmented into multiple smaller frequency bands (subcarriers) and data is transmitted in the individual subcarriers. The subcarriers are orthogonally and densely arranged on a frequency axis, which can achieve faster transmission and improve frequency utilization efficiency. The SC-FDMA scheme is a single-carrier transmission scheme where a frequency band is segmented for different terminals and the divided frequency bands are used by the different terminals for transmissions. According to the SC-FDMA scheme, not only can interference between the terminals be easily and effectively reduced but also variations of transmit power can be suppressed. As a result, the SC-FDMA scheme is preferred from some standpoints such as reduced power consumption for terminals and wider coverage.
In the future, the W-CDMA system and the LTE system may coexist at least in a time period, and there is a likelihood that a dual mode terminal capable of operating in the both systems may be utilized. Since the W-CDMA system and the LTE system use different radio access technologies, they may be operated separately from each other.
Meanwhile, the LTE system may be particularly preferred from the standpoint of fast or large capacity data communications while the W-CDMA may be preferred in voice data communications. However, if both systems are operated separately, it could not be expected to make efficient use of radio resources in consideration of these characteristics.